The invention is directed to a tool for maintaining two boards in spaced relative relationship to each other, as for example, deck boards or similar wooden boards incident to nailing during the building of a wooden deck, patio, walkway or the like. Typical of spacers for spacing two boards are disclosed in U.S. Pat. No. 3,735,497 (Boettcher) and U.S. Pat. No. 4,955,142 (Rieck). The latter patents each discloses structure for accomplishing the broad concept of board spacing, but each includes the disadvantage of preventing the worker or other person using the spacer from viewing and thereby ascertaining the position of the deck board edges relative to the spacer. Without such visual assurance a workman cannot be certain that the deck board edges contact the spacer and, therefore, cannot be assured that once the deck boards are nailed, the spacing between all adjacent deck boards will be identical. Though a slight deviation between adjacent deck boards is relatively inconsequential, should such occur with some consistency, the overall appearance of the eventually completed wooden deck, walkway or the like will lack uniformity, will not appear "square" to the eye and will be otherwise unaesthetic.